Photoresist

Figure 8.9 Typical process flow
in a photolithography step.
1) Dehydration bake at 150-200 ºC in vacuum or
nitrogen atmosphere for removing surface moisture
on wafer to improve PR adhesion
2) Wafer is primed with Hexamethyldisilazane
(HMDS) - a commonly used adhesion promoter
3) PR is applied by spin coating: small amount of
resist dispensed on wafer and the wafer chuck
(platform) spins rapidly (2000-6000 rpm)
1
T R
∝
ω
4) Softbake (prebake) at ∼ 90-100 ºC will help to
evaporate solvents in the resist
5) Exposure to optical source
6) PEB may be done to stabilize resist
7) Spray coating, or immersion, of wafer in
developer promotes PR removal in certain areas
8) Hardbake increases adhesion of PR to underlying
film to stabilize resist against the etch step or ion
implantation steps